• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.206-209
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• 2002

The fixed abrasive pad(FAP) has been introduced in chemical mechanical polishing(CMP) field recently. In comparison with the general CMP which uses the slurry including abrasives, FAP takes advantage of planarity. resulting from decreasing pattern selectivity and defects such as dishing due to the reduction of abrasive concentration especially. This paper introduces the manufacturing technique of $Al_2$O$_3$-FAP using hydrophilic polymers with swelling characteristic in water and explains the self.texturing phenomenon. It also focuses on the chemical effects on tungsten film and the FAP is evaluated on the removal rate as a function of chemicals such as oxidizer, catalyst, and acid. The removal rate is achieved up to 1000A1min as about 70 percents of the general one. In the future. the research has a plan of the advanced FAP and chemicals in tungsten CMP considering micro-scratch, life-time, and within wafer non-uniformity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.245-249
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• 2002

Tungsten carbide microshaft is used as various micro-tools in MEMS because it has high hardness and good rigidity. In this study, experiments were performed to produce tungsten carbide microshaft using electrochemical machining. $H_2SO_4$solution was used as electrolyte because it can dissolve tungsten and cobalt simultaneously. Optimal electrolyte concentration and machining voltage satisfying uniform shape and large MRR of workpiece were found. For one-step machining, the immersion depth over 1 mm was selected for avoidance of concentration of electric charge at the tip of the microshaft. The limit diameter with good straightness was shown and an empirical formula for WC-microshaft machining was suggested. By controlling the various machining parameters, a straight microshaft with 30 $\mu\textrm{m}$ diameter, over 1 mm length and under 0.5$^{\circ}$ taper angle was obtained.

• Proceedings of the Korean Reliability Society Conference
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• 2004.07a
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• pp.129-137
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• 2004

This paper presents an accelerated life test for burnout of tungsten filament of incandescent lamp. From failure analyses of field samples, it is shown that their root causes are local heating or hot sports in the filament caused by tungsten evaporation and wire sag. Finite element analysis is performed to evaluate the effect of vibration and impact for burnout, but any points of stress concentration or structural weakness are not found in the sample. To estimate the burnout life of lamp, an accelerated life test is planned by using quality function deployment and fractional factorial design, where voltage, vibration, and temperature are selected as accelerating variables. We assumed that Weibull lifetime distribution and a generalized linear model of life-stress relationship hold through goodness of fit test and test for common shape parameter of the distribution. Using accelerated life testing software, we estimated the common shape parameter of Weibull distribution, life-stress relationship, and accelerating factor.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.1
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• pp.81-90
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• 1990

In this study, ion beam deposited tungsten thin film for gate material of GaAs SAGFET(Self Aligned Gate FET) was annealed from 800\ulcorner to 900\ulcorner using RTA and detailed investigations of structural and electrical characteristics of this film were carried out using four-point probe, XRD, SEM, AES and current-voltage measurement. Investigated results showed phase of as deposited tungsten film was fine grain \ulcornerphase and phase tdransformation of this film into \ulcornerphase occured at annealing condition of 900\ulcorner, 6sec. But regardless of phase transformation, electrical characteristics of tungsten film were very stable to 900\ulcorner and in case of 900\ulcorner, 4sec annealing condition Schottky barrier height obtained from 10 diodes measurements was 0.66 + 0.003 eV.

• Solar Energy
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• v.16 no.2
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• pp.87-96
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• 1996

Electochromic tungsten oxide thin films were prepared on the ITO coated glass by rf magnetron sputtering from a compressed powder tungsten oxide target in an argonoxygen atmosphere. The influence of the preparation conditions, especially the substrate temperature, on the chemical stability of film was investigated. These films were cycled in 0.6M $LiClO_4$ and 0.6M $H_2SO_4$ electrolyte respecitively, and exhibited electrochromic behavior upon the electrochemical insertion and extraction of ion. Among these tungsten oxide thin films, films prepared at a substrate temperature of $150^{\circ}C$ were found to be most stable in terms of cyclic durability.

• Journal of the Korean Chemical Society
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• v.7 no.2
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• pp.186-188
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• 1963

An attempt to improve the method of volumetric determination of tungsten developed by Luke has been made successfully. Using amalgam coated lead instead of pure metallic lead in the reduction procedure. W(VI)-W(III) reduction has been found to be quantitative in rather concentrated hydrochloric acid. Since there was no excessive dissolution of lead via reduction of hydrogen ion, lead surface was totally accessible for the reduction of tungsten and no trouble was caused by dereposition of $PbCl_2$ crystals at the nozzle of Jones reductor. Furthermore, it has been confirmed that almost 100 mg. of $WO_3$ can be handled easily if the chloride concentration of the HCl is increased by adding solid $NH_4Cl$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1155-1156
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• 2006

Hopkinson bar dynamic test under strain rates ranging from 2000 $s^{-1}$ to 8000 $s^{-1}$ at room temperature revealed that the flow stress of tungsten heavy alloys depended strongly on the strain, strain rate, and the content of molybdenum. The variation of flow stress was caused by the competition between work hardening and heat softening in the materials at different strain rates. The high temperature strength of the matrix phase was increased by the addition of molybdenum, which enhanced the strength of the tungsten heavy alloys in high strain rate test.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1225-1226
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• 2006

Particles of high strength material when coated with silver offer a means of obtaining desirable electrical properties and high strength. The coating process employed aqueous ammoniacal silver-nitrate electrolytes with a formaldehyde solution as the reductant. Modifying additives were also applied. The reduction and subsequent deposition of silver occurred selectively on the surface of the tungsten particles. The morphologies of the coated particles were assessed by SEM imaging. The silver was uniformed coated on tungsten powder and its thickness was estimated to be approximately 100nm on the basis of a mass account.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.2
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• pp.156-161
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• 2004

We investigated the effects of oxidizer additive on the performance of Cu-CMP process using commonly used tungsten slurry. In order to compare the removal rate and non-uniformity as a function of oxidizer contents, we used alumina-based tungsten slurry and copper blanket wafers deposited by DC sputtering method. According to the CMP removal rates and particle size distribution, and the microstructures of surface layer by SEM image as a function or oxidizer contents were greatly influenced by the slurry chemical composition of oxidizers. The difference in removal rate and roughness of copper surface are believed to cause by modification in the mechanical behavior of $Al_2$O$_3$abrasive particles in CMP slurry.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.6
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• pp.105-112
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• 2007

Tungsten wire micro electrochemical machining (W-wire micro ECM) with ultra-short pulses enables precise micro machining of metal. In wire micro ECM, platinum wire has been used because it is electrochemically stable. However, the micro metal wire with low strength is easily deformed by hydrogen bubbles which are generated during the machining. The wire deformation decreases the machining accuracy. To reduce the influence of hydrogen bubbles, in this paper, the use of tungsten wire was investigated. To improve machining accuracy, suitable pulse conditions which affect generation of bubbles were also investigated. The tungsten wire micro ECM can be applied to the fabrication of various shapes. Using this method, various micro-parts and shapes were fabricated.